Study of gold nanorods–protein interaction by localized surface plasmon resonance spectroscopy

Abstract

In this paper, gold nanorods' (GNRs) interaction with different proteins (i.e. carbonic anhydrase, lysozyme, ovalbumin and bovine serum albumin (BSA)) at physiological pH is investigated using localized surface plasmon resonance (LSPR) spectroscopy. We observe that the incubation of these proteins at different concentrations with cetyltrimethylammonium bromidecapped GNRs of three aspect ratios induces dramatic changes in the extinction spectra of the nanoparticles. In particular, we correlate the position and shape of the longitudinal LSPR peaks to the ability of the proteins to specifically interact with GNRs' surface. The different types of behaviour observed are explained by the exposed molecular surface area of the proteins' cysteine residues as modelled on the basis of their respective X-ray crystallographic data structures. Cysteine is the only amino acid that exhibits an SH group that is well known to have a strong affinity to gold. The presence and the accessibility of such a residue may explain the protein binding to GNRs. The isoelectric point of the proteins is also an important characteristic to take into account, as the electrostatic strength between GNRs and protein explains some of the cases where aggregates are formed.

Adsorption of Organophosphate Pesticide Dimethoate on Gold Nanospheres and Nanorods

“…Regarding the fact that no red shift of longitudinal SRP was observed which indicates no side-to-side nanorods interaction and even though blue shift occurred but not corresponding growth of band at 520 nm there are no indication of end-toend nanorods interaction. Moreover, we observe that after 24 hours of nanorods incubation with dimethoate the width of the bands was constant (Figure 1(c), trace D), indicating a good dispersion of the nanoparticles in the solution which confirmed that no aggregation occurred [34][35][36]. The same behavior of NRs was noticed after 24 hours of their incubation with different concentrations of dimethoate (Figure 2(b)).…”

“…As dimethoate is neutral compound, stable in acid to neutral conditions with one sulphur atom accessible for interaction, while CTABcapped nanorods are positively charged, we suppose that dimethoate can only weakly adsorb on the CTAB double layer through electrostatic forces and not on the AuNRs' surface. Moreover, as the CTAB is preferentially bound onto lateral facets of nanorods, leaving the ends uncoated [35], there is a probability for the dimethoate to covalently bind on the nanorod ends. These changes of the AuNRs environment could explain LSRP slight blue shift (Figure 1(b)).…”

Optical Aggregation of Gold Nanoparticles for SERS Detection of Proteins and Toxins in Liquid Environment: Towards Ultrasensitive and Selective Detection

“…Considering that the dimension observed at this concentration is ~60 nm, we probably have the formation of a protein multilayer around the NRs surface. Decreasing the concentration, the resonance remarkably red shifts and broadens ( Figure 4 a blue, green, orange, magenta, brown lines), likely due to coupling effects among NRs that form aggregates very rapidly (few minutes or less) [ 46 , 69 ]. We phenomenologically describe the resonance profiles of such a system with a two-component Gaussian, one peaked at ~540 nm and a second one red-shifted and broadened.…”

“…At lowest concentrations (1 µM–50 nM), the quantity of protein is insufficient to cover the BIO-NRCs surface, provoking a continuous size increase of the aggregates, a process that ends up with precipitation of the structures. Aggregation of gold NRs upon addition of µM quantities of BSA was observed [ 69 , 71 ] and attributed to an unfolding of the BSA at the NRs surface followed by hydrophobic patch assembly [ 71 ]. An estimation of the number of proteins attached to the NRs can be carried out applying the “difference-volume” method reported in Refs.…”

Optical Nano Antennas: State of the Art, Scope and Challenges as a Biosensor Along with Human Exposure to Nano-Toxicology

“…The resonantly excited nanostructures behave as optical antennas similar to RF antennas, especially in IR (infrared) that concentrate the energy of electromagnetic radiation to a confined volume of the sub-wavelength scale. Thus, nanorods, with µm-sized lengths L that show plasmonic resonances in the IR spectral range [ 53 , 54 , 55 ] are termed nanoantennas. However, the simple λ/2-dipole behavior known from RF antennas, where the relationship between L and the resonant wavelength λ res is given by 2 L = λ res , does not hold for nanoantennas at optical frequencies.…”